In a fuel cell system, an oxidant gas (e.g., air) and a fuel gas (e.g., hydrogen) are supplied to a fuel cell, and electric power is generated through an electrochemical reaction of these reactant gases. Water that is generated in the fuel cell caused by this electrochemical reaction is discharged to the outside through an exhaust system of the fuel cell while the fuel cell system is in operation. However, when the outside-air temperature is low, the moisture inside the exhaust system freezes, and it may not be possible to continue the operation or restart the operation once it has been stopped. In order to solve such a problem, in the Patent Document 1 below, two exhaust systems with paths of small cross-sectional areas are provided such that it is possible to continue or restart the operation by ensuring an exhaust path in one of the exhaust systems even if the other one of the exhaust systems is frozen. However, since the gas is always exhausted from two systems, there is a problem in that the amount of electric power generation requested to the fuel cell cannot be ensured depending on the state of the fuel cell system.
In order to solve this problem, in the Patent Document 2 below, a plurality of exhaust systems that allows the reactant-off gas discharged from the fuel cell to flow is provided, as well as a control unit that selects, from a plurality of exhaust systems, the exhaust system that allows the reactant-off gas to flow depending on the state of the system is also provided.